A personal-computer-based software system to pacemaker-modified ECGs has been developed. Digital signal processing identifies cardiac events from intracardiac electrograms, surface ECGs, and pacemaker generated activity indicators. The pacemaker's functional status at each event is analyzed by a rule-based monitor model based on a software design model. Using this status information, an expert system identifies problems as well as their possible causes and potential solutions. Rule-like structures can be used to model the functioning of digital pacemakers. These design models serve as the basis for the system to analyze the functioning of the implanted pacemaker. These models are also of value during the pacemaker design phase. They reduce design time and improve the rigor, completeness, and audit trail of the design. In a proper computer environment, they can simulate the pacemaker for design testing, and can provide executable code for prototype testing.